The present invention relates to a method of treating surfaces on a magnetic head disk drive suspension, and in particular, to laser treating operative surfaces of head lift pads and load point dimples on a head suspension.
In a dynamic rigid disk storage device, a rotating disk is employed to store information. Rigid disk storage devices typically include a frame to provide attachment points and orientation for other components, and a spindle motor mounted to the frame for rotating the disk. A read/write head is formed on a xe2x80x9chead sliderxe2x80x9d for writing and reading data to and from the disk surface. The head slider is supported and properly oriented in relationship to the disk by a head suspension that provides both the force and compliance necessary for proper head slider operation. As the disk in the storage device rotates beneath the head slider and head suspension, the air above the disk also rotates, thus creating an air bearing which acts with an aerodynamic design of the head slider to create a lift force on the head slider. The lift force is counteracted by a spring force of the head suspension, thus positioning the head slider at a desired height and alignment above the disk that is referred to as the xe2x80x9cfly height.xe2x80x9d
Typically, the magnetic head is about 0.02 microns away from the disk while the disk is moving. In most disk drives it is important for the magnetic head and disk surface not to come in contact when the disks are not rotating (i.e., when the hard drive is not powered). If a disk and magnetic head are at rest and in contact for a period of time, the head and disk surface can stick together, resulting in damage to the disk surface when the disks start to rotate. In some cases the stiction force can prevent the disks from rotating altogether. Also, the disk must start from rest, and a certain minimum velocity is required for the magnetic head to float over the disk surface. Therefore, each startup of the hard drive can result in the magnetic head and disk surface rubbing for a distance until the disk achieves sufficient speed to form the air cushion.
For these reasons, load/unload ramp structures have been used in some hard drives to hold the magnetic heads away from the disk surfaces while the hard drive is not operating. The magnetic heads are released from the ramp structure when the disks have achieved the minimum speed for causing the magnetic heads to float above disk surfaces.
FIG. 1 shows a typical load/unload type hard drive with three disks 2. An actuator arm 3 supports a suspension 4, a slider 5 and a lift tab 6. A magnetic read/write head (not shown) is located on a bottom surface of the slider 5. The suspension 4 and slider 5 together comprise a head gimbal assembly. The actuator arm 3 pivots about a pivot post 9. The lift tab 6 is positioned on the suspension 4 so that it engages a ramp 8 on a ramp structure 10. The ramp 8 imparts an upward force on the lift tab 6, which lifts the slider 5 and magnetic head away from the disk 2. The magnetic head is thereby not in contact with the disk 2 whenever the lift tab 6 is moved onto the ramp 8. In order for the lift tab 6 to lift the slider from the disk, the lift tab must rub against the ramp 8. The ramp structure 10 is typically made from low-friction polymer materials. Low friction ramps 8 reduce the amount of energy required to unload the magnetic heads (a concern during unpowered unloading).
Lift tabs are typically made of metal such as stainless steel. Since they are harder than the ramp structure (made of plastic), the lift tab may abrade the ramp during loading and unloading. Abrasion creates contaminate particles within the hard drive that can damage the sensitive slider/disk interface. It is therefore necessary for the bottom lift tab surface (which contacts the ramp) to be as smooth as possible. A smooth lift tab surface produces fewer particles when rubbed over the surface of the ramp.
In addition to lift tabs, certain types of head suspensions include a generally spherical dimple having a convex surface formed in either the load beam or the cantilever region of the flexure, such as disclosed in U.S. Pat. No. 6,078,470 (Danielson et al.). FIGS. 2 and 3 illustrate a head suspension assembly comprising a head suspension 61 with a load point dimple and a head slider 69. The head suspension 61 includes a load beam 62 and a flexure 64 on a distal end of load beam 62. Load beam 62 is generally comprised of a mounting region 63 on a proximal end of load beam 62, a rigid region 68, and a spring region 67 between mounting region 63 and rigid region 68.
Mounting region 63 further includes base plate 63a, secured to load beam 62 by conventional means such as spot welds, and mounting structure 63b for mounting head suspension 61 to a rotary actuator of a rigid disk drive (see FIG. 1). Mounting structure 63b enables head suspension 61 to be positioned over an associated disk so the head can read data from or write data to the disk during the normal operation of the disk drive. Spring region 67 generally includes a bend or radius to provide a spring force used to counteract the aerodynamic lift force acting on flexure 64 in use. Rigid region 68 transfers the spring force from spring region 67 to a load region 68a at the distal end of load beam 62. Load region 68a then transfers the spring force to flexure 64.
Flexure 64 includes a cantilever region 65 having a slider mounting surface to which a head slider 69 is mounted. A free end 65a of the cantilever region is movable vertically in response to pitch and roll movements of the head slider 69 and cantilever region 65. Flexure 64 further includes arms 65b and 65c that extend longitudinally from a proximal end of flexure 64 to a cross piece 65d on a distal end of flexure 64. Offset bends 66a and 66b are located in cross piece 65d of flexure 64 to provide a planar mounting region for head slider 69 and an offset between cantilever region 65 and arms 65b and 65c. 
Dimple 66 is formed in cantilever region 65 of flexure 64, and dimple 66 confronts load region 68a of load beam 62. Dimple 66 provides a specific manner by which the spring force of spring region 67 is transferred from load region 68a of load beam 62 to cantilever region 65 of flexure 64, and furthermore, permits pitch and roll movements of the cantilever region 65 and head slider 69 as described in greater detail below. The dimple 66 acts as a xe2x80x9cload pointxe2x80x9d between the flexure/head slider and the load beam, and dimples designed to serve this purpose are referred to as xe2x80x9cload point dimplesxe2x80x9d.
A load point dimple provides clearance between the flexure and the load beam, and serves as a point about which the head slider can gimbal in response to the aerodynamic forces generated by the air bearing. Variations in the rotating disk create fluctuations in these aerodynamic forces. The aerodynamic forces cause the head slider to roll about a longitudinal axis of the head suspension, and to pitch about an axis planar with the head suspension but perpendicular to the longitudinal axis. The load point dimple serves as the pivot point about which the flexure and head slider gimbal in response to the pitch and roll aerodynamic forces.
Lift tabs and load point dimples that are stamped or coined from sheet metal have a number of limitations. The extreme pressure used to stamp the parts causes the die surface to degenerate through metal transfer. The area of highest pressure can become rougher than it was before the stamping or coining operation. Because of the nature of the coining process, the highest pressure is typically at the apex of the feature, which is typically the operative surface. Features smoothed by the coining process still produce debris when rubbed, such as against a ramp or a tang in a gimbal assembly, causing particulate contamination inside the disk drive and hence reduced reliability.
Stamping and coining processes generate excess debris and increase the variation in the location and geometry of the load point dimple. In addition to stamping and coining, load point dimples can be xe2x80x9cfree formedxe2x80x9d using a punch without a coining die. The punch is shaped to form the inside diameter of the load point dimple. Punch formed features tend to have rough surfaces due to the material being stretched during the forming process. A rough surface on a load point dimple can reduce gimbaling performance due to higher friction.
The present invention relates to a method of using pulsed laser energy to treat operative surfaces on lift tabs and load point dimples on a magnetic head disk drive suspension. The present method produces very smooth surfaces at a relatively low cost. The process is scalable for volume production. The present method can be used with operative surfaces having a wide variety of structures and shapes. The process provides for reduced particulate contamination inside a data storage hard drive, leading to higher reliability. In load point dimples, the reduced friction due to the smooth surfaces improves gimbaling. The present method of treating load point dimples also creates a more uniform geometry that reduces position variation caused during forming.
In one embodiment, the method of treating an operative surface includes patterning a laser beam such that a single pulse extends across the entire operative surface and applying one or more pulses of the laser energy to the operative surface sufficient to melt the operative surface. The melting serves to polish, smooth and/or reshape the operative surface.
The melting of the operative surface is typically to a depth of about 0.5 micrometers. The melting of the operative surface continues until a Ra surface roughness of about 100 to about 120 nanometers or less is achieved. The pulsed laser energy typically comprises a duration of about 1 to about 10 milliseconds. The entire operative surface preferably is melted simultaneously.
In one embodiment, the method includes determining a fluence and pulse duration such that a single pulse just starts to melt the tops of surface irregularities on the operative surface and repeating the pulse at a very rapid rate to achieve the desired level of polishing.
The present invention is also directed to a method for treating an area of a surface of a metal lift tab or load point dimple, wherein the surface has surface roughness features with a characteristic depth, the method comprising the step of: a) heating the area with an energy pulse having a power density sufficient to cause melting of the surface, wherein the heating is performed for a duration sufficient to melt the surface to a depth greater than the characteristic depth of the surface roughness features, and wherein the area is melted to a depth of less than 1.0 micrometers; b) cooling the area so that the area freezes.
In one embodiment, a mask is interposed between the source of the pulsed laser energy and the operative surface. The mask includes an aperture adapted to shape the laser energy to a shape generally corresponding to a shape of the operative surface. In some embodiments, the laser energy is directed through one or more lens located between the mask and the operative surface.